Prediction of remaining lifetime of superheater/reheater tubes in boilers burning high-sulfur coal
The secondary superheater and reheater tubes in steam boilers are susceptible to a form of accelerated corrosion which is related to the formation of complex sulfates of sodium, potassium, and iron which may have melting temperatures as low as 552/sup 0/C. The conditions required for this form of corrosion to occur include the deposition on the tubes of alkali- and sulfur- (and possibly iron-) containing species (from the coal), sufficient time and a temperature gradient in the deposit to allow the formation and migration of the corrosive species to the tube surface, and a tube surface temperature above the melting temperature of the complex sulfates. The factors that must be considered in a life expectancy calculation are: oxidation rate, molten salt corrosion rate, trisulfate melting point, original tube diameter, loss of outside diameter, internal scale thickness, and operating time. A computer program has been developed to carry out the life expectancy calculation based on these factors. This program was tested on the reheater of a 600 MW coal-fired boiler of General Public Utilities (GPU) which operates with 540/sup 0/C and 4.83 MPa reheat. Tube sections were removed from the vertical section of the reheater for evaluation. The output indicated that after 90,000 hours the tubes would be thinned to 3.4 mm (135 mils), which agreed with actual measurements. Tube failure was predicted at 108,000 hours, when the tube wall would be reduced to 2.8 mm (111 mils). In this case tube replacement within two years was recommended to avoid forced outages. 3 figures, 1 table.
- OSTI ID:
- 5542908
- Journal Information:
- Mater. Compon. Fossil Energy Appl.; (United States), Journal Name: Mater. Compon. Fossil Energy Appl.; (United States) Vol. 66; ISSN MCFAD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
014000* -- Coal
Lignite
& Peat-- Combustion
ALKALI METAL COMPOUNDS
BOILERS
CARBONACEOUS MATERIALS
CHEMICAL REACTIONS
COAL
COMBUSTION
COMPUTER CALCULATIONS
COMPUTERIZED SIMULATION
CORROSION
DEPOSITION
DEPOSITS
DIMENSIONS
ENERGY SOURCES
FOSSIL FUELS
FOULING
FUELS
IRON COMPOUNDS
IRON SULFATES
LOSSES
MATERIALS
MELTING POINTS
MOLTEN SALTS
OXIDATION
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POTASSIUM COMPOUNDS
POTASSIUM SULFATES
SALTS
SERVICE LIFE
SIMULATION
SODIUM COMPOUNDS
SODIUM SULFATES
SULFATES
SULFUR COMPOUNDS
SULFUR CONTENT
THERMOCHEMICAL PROCESSES
THERMODYNAMIC PROPERTIES
THICKNESS
TIME DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
TUBES